1. Field of the Invention
The present invention relates to a power transmission device that transmits electric power to a power receiving device by an electromagnetic induction method.
2. Description of Related Art
A power transmission device that transmits electric power to a secondary device in a non-contact manner by an electromagnetic induction method is already known.
In the power transmission device, when power transmission is started under the condition that a metallic foreign material is present, the transmitted electric power is absorbed by the metallic foreign material, which causes abnormal heating.
Therefore, in a technique for transmitting a certain amount of electric power, for example, a primary device and a secondary device each additionally includes a unit for sending and receiving signals between the primary device and the secondary device, and is configured to perform power transmission after determining whether or not the destination device is a normal device for power transmission.
For example, Japanese Patent Laid-Open No. 2006-74848 discloses technology in which a secondary unit that receives an electric power and a primary unit that transmits an electric power are each provided with an electromagnetic coupling coil for signal transmission. According to this technology, a signal that indicates that electric power is being received or for stabilizing a current and a voltage is fed back from the secondary unit to the primary unit at the time of power transmission.
Further, Japanese Patent Laid-Open No. 2000-134830 discloses a configuration in which a load sensor is provided in an electromagnetic induction power supply apparatus. According to this configuration, the load sensor can distinguish between a secondary power supply apparatus and a metallic foreign material, to thereby prevent abnormal heating due to the proximity of a metallic foreign material.
In order to send and receive signals between a primary device and a secondary device, a circuit configuration of each device is complicated. For example, in addition to a coil for power transmission, it is necessary to provide a coil or a circuit for sending and receiving signals.
Further, because it is necessary to provide each of the primary device and secondary device with a corresponding circuit or coil for sending and receiving signals, it is difficult to employ a power transmission device for transmitting electric power to a general power receiving device.